The present invention is generally directed to an apparatus for heat-sealing film materials. More particularly, the invention is directed to a platen having a segmented heating surface for heat-sealing a polymer film to an ink jet cartridge.
Various configurations of ink-containment vessels, tanks, and print heads for use in ink jet printers incorporate a pressure-regulating device for maintaining optimum ink pressure during operation of the printer. Many of these pressure-regulating devices typically comprise a polymer film covering a precision stainless steel ball disposed in an asymmetrical hole. The film is typically heat-sealed to a surface of the ink tank in order to hold the ball precisely in the hole, thereby forming narrow channels between the ball and the inside of the hole. The film may also cover a vent path in the tank. The ball typically protrudes slightly above the top edge of the hole so that the process of sealing the film over the ball applies a slight normal force to the ball, thereby holding it in a precise location within the hole. The surface to which the film is sealed is typically molded polypropylene or other polymer, or metal.
Due to the geometry and tolerances of the molded or formed tank material, and the geometry of the pressure-regulating device, the surface to which the film is to be sealed is usually not essentially planar. The planarity of the surface may vary by up to 0.2 mm. In the past, rigid platens, such as heated blocks of copper, have been used to heat-seal the film to the non-planar surfaces. Such rigid platens typically cause deformations in high spots of the sealing surface on the tank. This deformation can adversely affect the performance of the vent paths and narrow air channels in the pressure-regulating device.
The use of flexible or elastomeric material having a thickness sufficient to compensate for the non-planarity of the surface to be heated have not proved to be to be completely satisfactory.
Therefore, an improved heat-sealing platen is needed having a compliant heating surface that can accommodate the variations in height of the ink vessel and the pressure-regulating device.
The foregoing and other needs are met by a segmented platen for transferring heat into a film for heat-sealing the film to a non-planar surface of an ink jet printer cartridge. The platen includes a heat-transferring housing having sidewalls defining an internal cavity and a first aperture. A plurality of heat-transferring segments are disposed substantially within the housing and contacting the sidewalls of the housing. The segments partially protrude through the first aperture of the housing, and each segment has a heating surface disposed outside the cavity. Each of the segments is operable to independently move in relation to the housing and each other in a direction substantially parallel to the sidewalls of the housing. The platen includes a plurality of biasing devices disposed within the housing and corresponding in number to the plurality of heat-transferring segments. Each of the biasing devices independently urges a corresponding one of the segments through the first aperture, such that the heating surface of each segment is thereby urged to follow any curvature in the non-planar surface to which the film is applied when the platen engages the film. A heating element is disposed within the cavity and in contact with the housing. The heating element generates and transfers heat to the housing and the segments.
Thus, the present invention provides a segmented platen having heating surfaces that may move up and down independently of each other to accommodate any non-planarity in the surface to which the film is to be sealed. Each of the segments of the platen have high thermal conductivity, thereby transferring heat into the film material at a rate much higher than may be attained using existing compliant heated rubber platens. The independent movement and downward pressure of the segments upon the film provides efficient heat transfer into the film without deforming the high spots in the non-planar surface.
Preferred embodiments of the platen include a compliant metal shim disposed between the film and the lower heating surfaces of the segments. The shim prevents the edges of the segments from imprinting a grid-like pattern in the film.
In a preferred embodiment, the biasing devices provide differing levels of compressive force to the individual segments depending on the position of the segments within the platen, thereby providing different amounts of pressure to different locations on the film. This position-dependent variation in downward pressure is useful in sealing film over certain types of surface defects or irregularities in an ink jet cartridge, such as sink marks.
In another aspect, the invention provides a platen for heat-sealing a film to a non-planar surface. The platen includes a heating body containing a heating element. The platen also includes a plurality of independently-urgeable elements having non-elastomeric heating surfaces pending from the heating body and contacting the non-planar surface. The platen further includes urging devices corresponding to each of the independently-urgeable elements for urging the independently-urgeable elements toward the non-planar surface.